A cyclotron for accelerating ions (charged particles) in an outward spiral using an electric field impulse from a pair of electrodes and a magnet structure is disclosed in U.S. Pat. No. 1,948,384 (inventor: Ernest O. Lawrence, patent issued: 1934). Lawrence's accelerator design is now generally referred to as a “classical” cyclotron, wherein the electrodes provide a fixed acceleration frequency, and the magnetic field decreases with increasing radius, providing “weak focusing” for maintaining the vertical phase stability of the orbiting ions.
Among modern cyclotrons, one type is a class characterized as being “isochronous,” wherein the acceleration frequency provided by the electrodes is fixed, as with classical cyclotrons, though the magnetic field increases with increasing radius to compensate for relativity; and an axial restoring force is applied during ion acceleration via an azimuthally varying magnetic field component derived from contoured iron pole pieces having a sector periodicity. Most isochronous cyclotrons use resistive magnet technology and operate at magnetic field levels from 1-3 Tesla. Some isochronous cyclotrons use superconducting magnet technology, in which superconducting coils magnetize warm iron poles that provide the guide and focusing fields for ion acceleration. These superconducting isochronous cyclotrons can operate at field levels below 3 Tesla for protons and up to 3-5 Tesla when designed for accelerating heavier ions. The present inventor worked on the first superconducting cyclotron project in the early 1980's at Michigan State University.
Another class of cyclotrons is the synchrocyclotron. Unlike classical cyclotrons or isochronous cyclotrons, the acceleration frequency in a synchrocyclotron decreases as the ion spirals outward. Also unlike isochronous cyclotrons—though like classical cyclotrons—the magnetic field in a synchrocyclotron decreases with increasing radius. Synchrocyclotrons have previously had warm iron poles and cold superconducting coils, like the existing superconducting isochronous cyclotrons, but maintain beam focusing during acceleration in a different manner that scales to higher fields and can accordingly operate with a field of, for example, about 9 Tesla.